Abstract

A pump‐probe, light by light deflection technique employing 120 fs pulses at λ=620 nm has been used to measure the temporal and irradiance (I) dependence of the refractive index (n) in 100‐μm‐thick single crystals of CdS0.75Se0.25 and CdS at 295 K. For I<3 GW/cm2 only instantaneous negative changes in n are observed and are attributed to Stark and two‐photon resonance effects while for higher I negative changes with onset times of approximately 2 ps are attributed to the cooling of two‐photon generated carriers. For I≳30 GW/cm2 a partial recovery of n occurs within 10 ps and is attributed to possible threshold dependent recombination processes. The variation of probe‐beam deflection with pump irradiance has been determined for different probe delays and related to two photon absorption of the pump beam.